This is my Public Service Announcement.
Problem solved.
Turns out the solution for me is to disconnect from my home Wifi, connect with mobile hotspot to Sign-in to Lightroom on my ipad, and continue to do everything else with my home Wifi.
Strange, but my Mac, Pc, iPhone can all Sign-in fine using my home wifi. And it is on private.
I worked this out myself which chatting with adobe's live chat on this link (Thanks @Theresa_J for letting me know there's such a th